G protein-coupled receptors (GPCRs) allow transmission of local and long distance signalling within the body. They are responsible for cellular recognition of the physical senses such as taste, olfaction and sight as well as signal transduction of hormones and neurotransmitters. Over 850 GPCRs have been identified in the human genome all of which share a common structural element of seven transmembrane lipophilic moieties.1
Class C GPCRs function as homo- or hetero-dimers and are characterized by possession of large N-terminal ligand binding domains which exhibit a venus fly trap binding module.2 The class C taste receptors T1Rs, function only as heterodimers – the umami taste is T1R1/T1R3 and the sweet taste is T1R2/T1R3.3 The venus fly trap module of T1R2/T1R3 contains the orthosteric ligand binding site for sugars. A variety of sweet-tasting molecules exist which share no common structural features with sugar, these activate the receptor by allosteric means.
Allosteric activation and modulation of taste receptors, including the sweet-taste receptor have been investigated. In-vitro cell-based assays were performed using HEK-293 cells stably expressing Ga15-Gust protein co-transfected with hT1R2 and hT1R3. Various binding and functional assays were performed using radiolabelled and fluorescent signals to track binding to and activation of the receptor. The effect of cyclodextrins on the activation of the receptor was investigated.